Vulcanized or cured rubber articles made from most rubber-forming unsaturated polymers are known to be susceptible to attack by oxygen, ozone and ultra-violet radiation. Vulcanizates of natural rubber, synthetic polyisoprene, acrylonitrile-butadiene (nitrile-butadiene rubber, NBR) and styrene-butadiene (SBR), to name a few, are all susceptible to oxygen, ozone and ultra-violet attack. It is believed that this susceptibility is due to the presence of unsaturation in the rubber even after vulcanization. Some susceptibility exists in most conventional rubbers, even though antioxidants and antiozonants are routinely included in compounding recipes for making the vulcanizates.
Certain plastics and articles made therefrom are also known to be susceptible to ultra-violet (UV) light, and in some cases, also to oxygen and ozone. For example, polyethylene and styrene-maleic anhydride are known to be UV susceptible. (UV is a standard abbreviation for ultra-violet and will be used throughout the specification).
Polymers which are highly resistant to attack by oxygen, ozone and ultraviolet light are also known. One such class of polymers are those obtained by hydrogenating a conventional unsaturated polymer, e.g., a conjugated diene-containing polymer such as polyisoprene, styrene-butadiene copolymer (SBR) or a nitrile rubber (e.g., an acrylonitrile/butadiene copolymer, or NBR). U.S. Pat. No. 4,452,950 to Wideman discloses a hydrogenation process of this type, wherein an unsaturated polymer in latex form is hydrogenated with a combination of an oxidant (oxygen, air, hydrogen peroxide or a hydroperoxide), a reducing agent which is hydrazine or a hydrate thereof, and a metal ion activator. Much of the carbon-to-carbon unsaturation in the starting unsaturated polymer is reduced. Illustrative starting polymer latexes include nitrile rubber, (NBR), styrene/butadiene (SBR), polybutadiene (PBR) and styrene/vinylpyridine/butadiene terpolymer (vinylpyridine).
Other references disclosing hydrogenation of unsaturated conjugated diene-containing polymers are U.S. Pat. No. 4,384,081 to Kubo et al., U.S. Pat. No. 4,464,515 to Rempel et al., and British Patent No. 1,558,491.